1. Field of the Invention
The present invention generally relates to internal combustion (i.c.) engines and, in particular, to internal combustion engines having an increased lubrication oil capacity and/or gradiability.
Oil sumps on i.c. engines are required to contain oil for the lubricating requirements of the engine under a wide variety of engine operating conditions. The quantity of oil required to be contained in the sump depends upon a number of factors including the type of duty for which the engine is to be used, the shortest acceptable servicing interval, the engine size, the environment in which the engine is to be operated and the cooling effect of oil flowing through and around the components of the engine.
In particular, the constant move towards higher specific power outputs and wider servicing intervals places demands on the lubricating and cooling performance of the engine oil which are increasingly difficult to satisfy without enlarging the engine oil capacity. An increase in the oil capacity of an engine can benefit servicing intervals because there will be a larger volume to accept a given quantity of contaminants. A larger capacity can also reduce engine operating temperatures to the benefit of both oil life and engine components such as crankshaft bearings.
In modern diesel engines, it is known to retard fuel injection timing by predetermined amounts. This can lead to greater soot contamination of lubricating oil.
Increasing the oil capacity of the sump can redress this problem and even allow the service interval for oil changeover to be increased.
Enlarging the oil capacity by increasing the maximum level in a sump can, however, have very undesirable effects. The main problem is the increased possibility for windage, this being a tendency for the sweep of a crankshaft journal and its associated connecting rod big end to pick up oil from the sump and throw it around the inside of the engine, thereby increasing oil temperature, oil consumption and emissions and reducing engine efficiency. Windage can occur even where the sweep of the connecting rod big end is above, but close to, the sump oil level.
A commonly adopted practice to permit the raising of the maximum oil level in a sump, and thereby the oil holding capacity, is to provide a perforated baffle or `windage tray` between the crankshaft and the surface of the oil in the sump. However, whilst this will assist in reducing windage when the engine is running at a normal horizontal inclination, windage can still occur when the engine is inclined above the horizontal inclination or when inertial forces resulting from vehicle direction changes cause oil to translocate from beneath to above the baffle through its perforations.
2. Description of the Related Art
U.S. Pat. No. 3,100,028 teaches increasing the oil capacity of an i.c. engine by extending a lower portion of a sump in an outward direction. However, this increase in width inevitably leads to an increase in the engine envelope size and can result in the sump wings fouling the vehicle chassis or bodywork.
An alternative means of increasing the oil capacity of an engine whilst reducing the risk of windage is disclosed in U.S. Pat. No. 5,479,886 wherein it is taught to provide restrictions against oil return to the sump from upper regions of the engine so that these upper regions act as supplementary oil reservoirs during engine operation. The restriction to oil return to the sump from the upper regions is brought about by compelling the oil to negotiate a number of small diameter drain holes.
A further restriction to oil return is taught in U.S. Pat. No. 5,479,886, namely the inclusion, in upper regions of the engine, of oil retaining chambers from which oil cannot drain back to the sump irrespective of whether the engine is operating or not.
The teaching of this latter prior art reference has several drawbacks. Firstly, the small drain holes may become blocked with the products of combustion or other foreign material contaminating the oil and thus prevent oil returning to the sump. Secondly, when the engine is due for servicing it will have to stand for some considerable time after being operated to allow the oil to drain to a removal point. This standing time could be lengthy if the oil has not thoroughly warmed and is therefore of a high viscosity. There is therefore a risk of new oil being introduced before the old oil has been substantially removed. Thirdly, no means is disclosed in U.S. Pat. No. 5,479,886 to ensure that the oil deliberately trapped by the non-draining oil chambers is free of contaminants, such as the residues of combustion, which may be released into the `clean` lubricating oil subsequent to an oil change.
The problem of providing an engine with a high oil capacity is exacerbated by the requirement for some engines to operate at steep inclinations above the horizontal such as is experienced in earthmoving equipment or lifeboat vessels. The tendency for windage in an engine escalates as the angle of operation increases and will be particularly noticeable at a lower end of an inclined engine because the sump oil level will have been brought into closer proximity to the rotating crankshaft. In such a case, the maximum operating angle is dependent upon the angle at which windage will commence at a lower end of the engine.
A further problem is the difficulty in indicating to the operators of equipment the point at which the limit of allowable engine operating inclination has been reached. The limiting angle is commonly lower than the angle which an operator would wish to operate the equipment at, therefore the lower the designated maximum angle of operation, the greater the risk of it being exceeded. A comparatively low maximum angle not only restricts the use of the equipment but also increases the risk of abuse of the intended maximum angle and if this abuse introduces windage, it may well lead to overheating, increased emissions and increased oil consumption in the engine.